linux-kernel - Re: data-race in nf_tables_newtable / nf_tables

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Date:   Fri, 19 Aug 2022 14:35:42 +0200
From:   Florian Westphal <fw@...len.de>
To:     Abhishek Shah <abhishek.shah@...umbia.edu>
Cc:     coreteam@...filter.org, davem@...emloft.net, edumazet@...gle.com,
        fw@...len.de, kadlec@...filter.org, kuba@...nel.org,
        netdev@...r.kernel.org, netfilter-devel@...r.kernel.org,
        pabeni@...hat.com, pablo@...filter.org,
        Gabriel Ryan <gabe@...columbia.edu>,
        linux-kernel@...r.kernel.org
Subject: Re: data-race in nf_tables_newtable / nf_tables_newtable

Abhishek Shah <abhishek.shah@...umbia.edu> wrote:
> Hi all,
> 
> We found a race involving the table->handle variable here
> <https://elixir.bootlin.com/linux/v5.18-rc5/source/net/netfilter/nf_tables_api.c#L1221>.
> This race advances the pointer, which can cause out-of-bounds memory
> accesses in the future. Please let us know what you think.
> 
> Thanks!
> 
> 
> *---------------------Report-----------------*
> *read-write* to 0xffffffff883a01e8 of 8 bytes by task 6542 on cpu 0:
>  nf_tables_newtable+0x6dc/0xc00 net/netfilter/nf_tables_api.c:1221
>  nfnetlink_rcv_batch net/netfilter/nfnetlink.c:513 [inline]

[..]

> *read-write* to 0xffffffff883a01e8 of 8 bytes by task 6541 on cpu 1:
>  nf_tables_newtable+0x6dc/0xc00 net/netfilter/nf_tables_api.c:1221
>  nfnetlink_rcv_batch net/netfilter/nfnetlink.c:513 [inline]

[..]

I don't understand.  Like all batch operations, nf_tables_newtable is
supposed to run with the transaction mutex held, i.e. parallel execution
is not expected.

There is a lockdep assertion at start of nf_tables_newtable(); I
don't see how its possible that two threads can run this concurrently.